Some example embodiments relates to fluid pressure actuators.
For example, Japanese Patent Publication Application No. 2004-301138 discloses a fluid pressure actuator provided in a mounting head of an apparatus (e.g., die-bonder, mounter, etc.), which is used in a post-process of manufacturing a semiconductor chip. The mounting head is provided to mount semiconductor chip thereon, and the actuator enables load control and position control of the mounting head.
FIG. 1A is a schematic diagram showing a cross-sectional configuration of a fluid pressure actuator according to the related art. FIG. 1B is a diagram illustrating an operation of a controller included in a fluid pressure actuator according to the related art.
A fluid pressure actuator 90 shown in FIG. 1 includes a cylinder 10, a piston body 50, and a servo valve 60. The cylinder 10 includes a cylinder body 11, a guide flange or a housing 13, and a ball bearing 30. The piston body 50 includes a piston head 51 and a rod 52,
In the fluid pressure actuator 90, an axial direction sensor 41 (which includes an axial direction scale 41-1 and an axial direction detector 41-2) is configured to detect a position when the piston body 50 moves in an axial direction (e.g., Z direction shown in FIG. 1A). The axial direction sensor 41 is configured to output a detection signal ΦDZ indicating a position in the axial direction. Referring to FIG. 1B, a controller 80 is configured to control pressure within the cylinder 10 by using the servo valve 60 on the basis of the detection signal ΦDZ, and may control the position of the rod 52, serving as a movable portion, in the axial direction.
Further, a fluid pressure bearing portion (gap between the rod 52 and the guide flange 13) may have a polygonal shape and be configured to enable transmission of the rotation of a rotation motor 71 to the rod 52 in a non-contact manner, as shown in FIG. 2. For example, the rotation motor 71 (e.g., step motor, servo motor, etc.) may be provided outside the cylinder 10, and the rotation of the rotation motor 71 may be transmitted to the guide flange 13 through a timing belt 72 and a pulley 73, thereby rotating the rod 52. Thus, the controller 80 may control the rotation of the rod 52 based on a detection signal ΦDθ (which is a detection signal indicating a rotation angle the rotation motor 71 with respect to an axis of rotation), which is output from an encoder 75 provided in the rotation motor 71. Meanwhile, a hollow direct drive (DD) motor may be used as the rotation motor 71 so that the rotation of the rod is controlled without using the timing belt 72 and the pulley 73 with respect to the axis of rotation (e.g., Z direction) of the piston body 50.
According to the related art described above, the rotation of the rotation motor 71 is transmitted through the fluid pressure bearing portion having a polygonal shape, but an angular movement amount (which is an angle based on the rotation of the rod 52) of the rod 52 in a rotation direction of the rod is not taken account. The angular movement amount is detected using the encoder 75, which is included in the rotation motor 71 provided outside the fluid pressure actuator 90, as a position detector.
FIG. 2 is diagrams for explaining a problem of a fluid pressure actuator according to the related art. In FIG. 2, a diagram in the left shows a state where the rod 52 and the guide flange 13 that are not in motion and a diagram in the right shows a state where the guide flange 13 is rotated clockwise by an angular movement amount θ from the position by rotating the rotation motor 71.
As shown in FIG. 1A, an encoder 75 (e.g., a scale and a detector) is provided outside the cylinder 10. Accordingly, when the guide flange 13 is rotated by the angular movement amount θ, the rod 52 may be rotated with a rotation deviation amount 6 from the angular movement amount θ due to a gap between the rod 52 and the guide flange 13. For example, the gap may include a fluid pressure bearing portion. However, the encoder 75 provided in the rotation motor 71 provided outside the rod 52 may detect the angular movement amount θ of the guide flange 13, but may not detect an angular movement amount (θ+δ) of the rod 52 that includes a rotational deviation with the guide flange 13 of the rod 52.
Because the encoder 75 (e.g., scale and the detector) is provided outside the cylinder 10 (which is a rotation driving side), the encoder 75 cannot precisely detect an actual position of the rod 52 due to the gap between the rod 52 and the guide flange 13, in which, for instance, a fluid is interposed, operates an error factor. Accordingly, a mounting failure may occur, for instance, when bonding a bump to a miniaturized semiconductor chip (driven part coupled to the rod 52) by a rotation error caused by the error factor.